(420b) Development of Low-Temperature Electrolytes Consisting of Ionic Liquid and Organic Solvents for MET Seismometer

Ionic liquids (ILs) are materials consisting of asymmetric ions and thus can remain liquid at room temperatures. Their unique properties of wide liquidus range, low volatility, considerable conductivity, and excellent thermal and electrochemical stability have made them popular candidates as electrolytes in energy storage devices and sensors. Specifically, due to versatile designs of ILs and their complex interactions with solvents, properties of IL-based mixtures can be tailored to support operations under extreme environmental conditions that molecular liquids fail to achieve. Herein, we present development of iodide-containing low-temperature liquid electrolytes for molecular electronic transducer (MET) seismometer employed in space explorations of Ocean Worlds planets, where surface temperatures can be as low as -150 ËšC.¹ An IL with iodide as an anion was selected along with another iodide salt to provide electroactive species for the MET seismometer, and two electrolyte systems were designed correspondingly with incorporation of different classes of organic solvents.² Via spectroscopy characterization techniques (e.g., FTIR, NMR, and Raman), we validated the hypothesized hydrogen bonding between the organic solvent molecules and IL cations, which led to effective disruption of the predominant coulombic attractions between existing ions. Consequently, the optimized microscopic intermolecular interactions resulted in improvement of macroscopic characteristics such as thermal and transport properties. DSC thermograms indicated glass transition temperatures of -119 and -150 ËšC for the two electrolyte systems, respectively, without other undesired phase transitions. Compared to a previously developed electrolyte system of dual ILs/water mixture, we have successfully extended the lower temperature limit of electrolytes, making them more viable candidates for low-temperature applications.³ Viscosity and conductivity of the developed electrolytes were also examined via rheometer and EIS as a function of temperature from 25 to -75 ËšC, which disclosed the effects of respective organic solvents on low-temperature transport property evolution. Lastly, with an electrochemical sensing principle as premise, electrochemical stability of the electrolyte and redox behaviors of the electroactive species were also investigated. We anticipate the presented work to not only advance MET seismometer applications, but also provide a facile design strategy for low-temperature electrolyte developments.

References:

1. H. Huang, V. Agafonov and H. Yu, Sensors, 2013, 13, 4581–4597.
2. Y. Xu, W. J. Lin, M. Gliege, R. Gunckel, Z. Zhao, H. Yu and L. L. Dai, J. Phys. Chem. B, 2018, 122, 12077–12086.
3. W. J. Lin, Y. Xu, S. MacDonald, R. Gunckel, Z. Zhao and L. L. Dai, RSC Adv., 2019, 9, 36796–36807.